The preferred embodiment concerns a method for regulation of the optical density in an electrographic printing method as well as a toner layer thickness measurement system in an electrographic printer or copier.
In electrographic printing methods (which, for example, comprise electrophotographic, magnetographic or also ionographic printing methods), to achieve a desired optical density it is necessary to effect a specific layer thickness of the toner accumulated on the recording carrier material in the developing process.
Given printing with only one color, in particular given printing with black toner, a desired optical density can be achieved in a relatively trouble-free manner due to the strongly opaque character of black. However, given multicolor printing it is very important for a correct color reproduction that the individual colors correspond exactly to a predetermined optical density.
Density measurement sensors can be provided for measurement and regulation of the optical density in an electrographic printing apparatus. For example, measurement arrangements based on a capacitive principle with which the toner layer thickness of electrographically developed toner images or toner layers can be measured for this purpose are known from DE 101 51 702 A1 and from US 2003/0091355 A1.
An electrographic printing or copying apparatus in which a developer station is supplied with fluidized toner via a negative pressure system is known from WO 03/100520.
A printing apparatus in which a temperature and moisture sensor is provided and in which image recording parameters are corrected when the measured values lie outside of predetermined values is known from U.S. Pat. No. 6,463,226 B2.
Further printing apparatuses with a moisture sensor are known from U.S. Pat. No. 6,353,716 and US 2006/0152775 A1. An electrophotographic printing system with a device for estimation of the toner density in a developer mixture is known from US 2006/0018674 A1.
An electrographic printing apparatus in which the latent image is developed with fluid toner is known from US 2003/0175048 A1.
The aforementioned publications are herewith incorporated by reference into the present specification.